The Designer's Guide Community
Forum
Welcome, Guest. Please Login or Register. Please follow the Forum guidelines.
Mar 29th, 2024, 2:10am
Pages: 1 2 
Send Topic Print
Theory to design a pierce oscillator (tough question) (Read 3652 times)
Kevin Aylward
Community Member
***
Offline



Posts: 52

Re: Theory to design a pierce oscillator (tough question)
Reply #15 - Jul 10th, 2013, 9:30am
 
The laws of physics demand that the voltage across a resister is in phase with its current. Possibly simulator needs to be set with tighter tolerances, and more time points, or Ken has built in a deliberate error in Spectre to annoy people. The rest of the xtal is all lossless components, hence cannot dissipate any heating power. All power in the XTAL black box must therefore be due to the resistor.
Back to top
 
 

Kevin Aylward
View Profile WWW   IP Logged
Pictou
Junior Member
**
Offline



Posts: 22

Re: Theory to design a pierce oscillator (tough question)
Reply #16 - Jul 11th, 2013, 5:14am
 
Thank you for your help, it does make sense!

PS : your tutorial on startup circuit is really well written, thank you for sharing this.
Back to top
 
 
View Profile   IP Logged
loose-electron
Senior Fellow
******
Offline

Best Design Tool =
Capable Designers

Posts: 1638
San Diego California
Re: Theory to design a pierce oscillator (tough question)
Reply #17 - Aug 2nd, 2013, 7:31pm
 
Couple things on simulating with a high Q crystal -

The high Q will lead to errors in resolution due to the extreme narrowness of the resonance.
(you actually miss the peak of the curve in the frquency steps, unless you get really small and thus slow simulations)

This also leads to really slow start times for transient simulations.

Tricks:

Drop the Q down a lot in the crystal model, this will speed simulation and you won't need micro steps when frequency sweeping. This will also speed you start-up time as oscillation builds.

Other useful item - instant start of the simulation instead of waiting for it to slowly build up - put an initial condition of current on the inductor in the crystal model. This will give you an instant start for the crystal.

THis has been discussed here before.

Back to top
 
 

Jerry Twomey
www.effectiveelectrons.com
Read My Electronic Design Column Here
Contract IC-PCB-System Design - Analog, Mixed Signal, RF & Medical
View Profile WWW   IP Logged
Kevin Aylward
Community Member
***
Offline



Posts: 52

Re: Theory to design a pierce oscillator (tough question)
Reply #18 - Aug 3rd, 2013, 1:28am
 
It would be a good idea to set up a parameterised model of the xtal. A generic model would be like:

.SUBCKT XTAL 1 2 c1=1p esr=50 f=10M c0=2p
Cp 1 2 {c0}
Ls 1 3 {0.025330295/f/f/c1}
Cs 3 4 {c1}
Rs 4 2 {esr}
.ends

In Cadence you can use the CDF to set a parameterised symbol for a schematic block. The inductor inductance field can contain the equation. The Q can then be varied as desired by changing c1. Typical c1’s will be from  1ff to 20ff for full Q, and 1pf for sims that finish this week.
Back to top
 
 

Kevin Aylward
View Profile WWW   IP Logged
ricardo80
New Member
*
Offline



Posts: 1

Re: Theory to design a pierce oscillator (tough question)
Reply #19 - Nov 1st, 2013, 10:03am
 
@Pictou: I think your simulation is ok if it works well and there is problem in the calculation of the frequency and if it does not work well try to adjust the values of R,L and C because the frequency of oscillation of the oscillator depends upon the these parameters.
Back to top
 
 
View Profile   IP Logged
Pages: 1 2 
Send Topic Print
Copyright 2002-2024 Designer’s Guide Consulting, Inc. Designer’s Guide® is a registered trademark of Designer’s Guide Consulting, Inc. All rights reserved. Send comments or questions to editor@designers-guide.org. Consider submitting a paper or model.